Traditionally, commercial propagation of Pelargonium x domesticum (Regal Pelargoniums, or "Martha Washington Geraniums" as distinct from other geraniums) has been effected primarily if not exclusively by vegetative propagation of cuttings. Even though certain other plants may easily be propagated by in vitro tissue culture techniques, earlier attempts at reliable propagation of Pelargonium x domesticum by tissue culture have been unsatisfactory if not completely unsuccessful.
For example, as reported by Cassells, A.C., and Carney, B.F., "Adventitious regeneration in Pelargonium x domesticum Bailey," Acta Horticulturae, 212(II), 419-425 (1987), in stem and petiole tissue cultures of Grand Slam (as an example of P. domesticum), up to 16% of the adventitious regenerants were variants, depending on the explant origin. Controls, whether stem cuttings or in vitro nodal cultures, yielded no variants. The authors concluded that genome instability in Grand Slam and presumably other P. domesticum varieties may produce useful variation but mitigates against the use of adventitious regeneration in micropropagation.
These findings are consistent with the earlier work of Skirvin, R.M. and Janick, Jules, "Tissue Culture-induced Variation in Scented Pelargonium ssp.," J. Amer. Soc. Hort. Sci., 101(3), 281-290 (1976). Skirvin et al. compared tissue culture propagated Pelargonium plants (from root cuttings, petiole cuttings or calliclones) with plants derived from vegetative propagation, i.e., stem cuttings. The plants derived from stem cuttings were all uniform and identical to the parental clone, whereas those from the root cuttings, petiole cuttings or calliclones were all morphologically distinct with the degree of variability depending on the cultivar. The authors conclude that the variability associated with calliclones derived from tissue culture is a pool on which selection can be imposed, implying conversely that tissue culturing of this type is inappropriate for use in attempting reliable regeneration of Pelargonium x domesticum.
Accordingly, a need remains for a reliable and commercially viable tissue culture propagation technique for Pelargonium x domesticum varieties.